The conveyor in a signature machine may be of considerable length and there may be as many as thirty or forty hoppers from which the signatures are fed. The machine includes subcombinations such as inserters, trimmers, stitcher heads, mailers and diverters.
The conveyor on which the signatures are collected delivers the unbound books to stitcher heads at a stitching station. In a conventional arrangement, there are individual grippers at the stitching station which move the books stepwise through the stitching station in the direction of a diverter, trimmer, mailer or some other unit, any one of which will have its own drive connection, especially the trimmers. The grippers are carried by a long, heavy gripper support which is reciprocated by a gripper bar and because crank motion in the conventional arrangement is involved for reciprocating the gripper mass, harmonic motion is necessarily involved. Harmonic motion means vibration and indeed the two are equated in classic mechanics. In a large machine, this is a problem of considerable magnitude because the masses involved can cause the machine to shake and pulse. The present invention addresses these problems.
Others have addressed the problem and one solution proposed was to retime some of the chain drives. Retiming is theoretically an answer but in the practical sense this would more or less require constant supervision because the user frequently makes changes in timing to accommodate to book size, or when performing 3-knife or 5-knife trimming, or for other reasons. We have determined upon a different answer.